Phenol-formaldehyde resins are polymers prepared by reacting a phenol with an aldehyde in the presence of an acid or a base, the base-catalyzed phenolic resins being classified as resol-type phenolic resins. A typical resol is made by reacting phenol with an excess of formaldehyde, in the presence of a base such as ammonia, to produce a mixture of methylol phenols which condense on heating to yield low-molecular weight prepolymers, or resols. On heating of the resols at elevated temperature under basic, neutral, or slightly acidic conditions, a high molecular weight network structure of phenolic rings is produced, linked by methylene groups, and typically retaining residual methylol groups.
GB 1,347,878 discloses a process in which phenol or a phenol derivative is condensed with formaldehyde in aqueous solution, in the presence of a catalyst which is an organic or an inorganic base, and in a homogeneous phase, to obtain a resin in the form of a suspension of oily droplets in the reaction medium, the suspension being stabilized by the addition of a dispersing agent which prevents the coalescence of the droplets. The process described results in spherical beads of phenolic resin that may be separated, washed, and dried, that are said to be useful for a variety of purposes, for example as filling material or for lightening the weight of such traditional materials as cement or plaster.
GB 1,457,013 discloses cellular, spherical beads having a high carbon content, containing a plurality of closed cells, wherein the walls of the peripheral cells form a continuous skin marking the limits of the external surface. The beads may be comprised of an organic precursor material, which can be a phenoplast, and the process by which they are made includes a carbonization step.
U.S. Pat. No. 3,850,868 discloses reacting urea or phenol and formaldehyde in a basic aqueous medium to provide a prepolymer solution, blending the prepolymer in the presence of a protective colloid-forming material, subsequently acidifying the basic pre-polymer solution so that particles are formed and precipitated in the presence of a colloid-forming material, as spheroidal beads, and finally collecting and, if desired, drying the urea or phenol formaldehyde particulate beads. The resulting beads are said to have a high flatting efficiency making them suitable for low gloss coating compositions.
U.S. Pat. No. 4,026,848 discloses aqueous resole dispersions produced in the presence of gum ghatti and a thickening agent. The dispersions are said to have enhanced utility in such end-use applications as coatings and adhesives.
U.S. Pat. No. 4,039,525 discloses aqueous resol dispersions produced in the presence of certain hydroxyalkylated gums, such as hydroxyalkylated guar gums, as interfacial agents.
U.S. Pat. No. 4,206,095 discloses particulate resols produced by reacting a phenol, formaldehyde, and an amine in an aqueous medium containing a protective colloid, to produce an aqueous suspension of a particulate resol, and recovering the particulate resol from the suspension.
U.S. Pat. No. 4,316,827 discloses resin compositions useful as friction particles that include a mixture of tri- and/or tetrafunctional and difunctional phenols, an aldehyde, an optional reaction-promoting compound, a protective colloid, and a rubber. In a first step condensation reaction, the rubber can be incorporated either in the interior or incorporated on the surface of the resin particles. The condensation product is subjected to a second step under acidic conditions, which results in a product in particulate form that is said to require no grinding or sieving when used as a friction particle.
U.S. Pat. No. 4,366,303 discloses a process for producing particulate resol resins that comprises reacting formaldehyde, phenol and an effective amount of hexamethylenetetramine or a compound containing amino hydrogen, or mixtures thereof, in an aqueous medium containing an effective amount of a protective colloid for a sufficient time to produce a dispersion of a particulate resol resin; cooling the reaction mixture to below about 40° C.; reacting the cooled reaction mixture with an alkaline compound to form alkaline diphenates; and recovering from the aqueous dispersion a resin exhibiting increased cure rates and increased sinter resistance.
U.S. Pat. No. 4,182,696 discloses solid particulate, heat-reactive, filler-containing molding compositions that are directly produced by reacting a phenol, formaldehyde, and an amine in an aqueous medium containing a water-insoluble filler material having reactive sites on the surface thereof that chemically bond with a phenolic resin and protective colloid to produce an aqueous suspension of a particulate filler-containing resol, and recovering the filler-containing resole from the suspension. The filler materials may be in the form of fibrous or non-fibrous particles and may be inorganic or organic.
U.S. Pat. Nos. 4,640,971 and 4,778,695 disclose a process for producing a resol resin in the form of microspherical particles of a size not exceeding 500 μm by polymerizing phenols and aldehydes in the presence of a basic catalyst and a substantially water-insoluble inorganic salt. Preferred inorganic salts, which include calcium fluoride, magnesium fluoride, and strontium fluoride, partially or entirely cover the surface of the resulting microspherical particles.
U.S. Pat. No. 4,748,214 discloses a process for producing microspherical cured phenolic resin particles having a particle diameter of not more than about 100 μm by reacting a novolak resin, a phenol, and an aldehyde in an aqueous medium in the presence of a basic catalyst and an emulsion stabilizer. The novalak resin employed in the process is obtained by heating a phenol and an aldehyde in the presence of an acidic catalyst such as hydrochloric acid or oxalic acid to effect polymerization, dehydrating the polymerization product under reduced pressure, cooling the product, and coarsely pulverizing it.
U.S. Pat. No. 4,071,481 discloses phenolic foams, mixtures for producing them, and their processes of manufacture. The resin used is a base catalyzed polycondensation product of phenol and formaldehyde which is obtained in a solid, reactive, fusible, substantially anhydrous state. The resin is foamed and hardened by the application of heat without the use of a catalyst. Heat sensitive blowing agents, either in liquid form or in particulate form may be mixed with the resin prior to heating. Surfactants and lubricants may be utilized to enhance the uniformity of the voids in the foam. The resulting foams are said to be non-acidic, resistant to color changes, and substantially anhydrous.
U.S. Pat. No. 5,677,373 discloses a process for producing a dispersion, wherein dispersed slightly crosslinked polyvinyl seed particles are swollen with an ionizing liquid, the seed particles containing covalently linked ionizable groups causing a swelling of the seed particles by the ionizing liquid to form a dispersion of droplets, wherein the resulting droplets after the swelling have a volume which is at least five times that of the seed particles. The ionizing liquid may be or contain a polymerizable monomer or may be charged with such a monomer. Polymerization of the monomers is said to be effected in the droplets during or after the swelling, to form polymer particles.
CN 1240220A discloses a method for manufacturing a phenol-formaldehyde resin-based spherical activated carbon that includes mixing together a linear phenol-formaldehyde resin and a curing agent to form a block mixture, crushing the block mixture to form particles of a resin raw material, dispersing the resin raw material in a dispersion liquid that contains a dispersing agent, emulsifying the material to form spheres, and carbonizing and activating the resulting spheres.
JP 63-48320A discloses a method for manufacturing a particulate phenolic resin, in which a particulate obtained from a condensation product aggregating around a core substance is produced by subjecting a phenol and an aldehyde to a condensation reaction in the presence of a dispersant and the core substance. The particulate is then dehydrated and dried. The core substance can be either an organic or an inorganic material. The particulate material obtained is characterized as being relatively soluble in acetone.
JP 10-338511A discloses a spherical phenolic resin having a particle diameter from 150 to 2,500 μm obtained by condensing phenols and aldehydes in the presence of a dispersant with a nucleus material, by causing the condensation product to aggregate around the nucleus material. A phenolic resin, glass granules, SiC, mesophase carbon, alumina, graphic, and phlogopite, are said to be useful as nucleus material.
Spherical beads comprised of phenolic polymers may thus be made using various methods and have a variety of uses and, while for many uses the particle size and particle size distribution may not be especially important, for some uses, particle size may well be an important factor, for example, when a carbonized product is desired having particular transport or adsorption properties. It may also be important to obtain particles having a relatively narrow particle size distribution, for example when the bulk flow properties of a carbonized product are important, such as to facilitate flow of the particles, or when predictable packing of the particles is necessary or helpful.
For example, U.S. Patent Publication No. 2003/0154993A1, which discloses cigarettes that include a tobacco rod and a filter component having a cavity filled with spherical beaded carbon, emphasizes the importance of obtaining point-to-point contact between the spherical beads together with substantially complete filling of the cavity so as to produce minimal channeling of ambulatory gas phase as well as maximum contact between the gas phase and the carbon surface of the spherical beads during smoking.
For these and other uses, obtaining a desired particle size and shape and particle size distribution may be an important factor in the economic viability of a spherical polymer bead in the marketplace. There remains a need in the art for resol beads useful in a variety of products, that overcome the various disadvantages of those presently known in the art.